National Semiconductor LM3687 Technical data
July 7, 2008
LM3687
Step-Down DC-DC Converter with Integrated Low Dropout
Regulator and Startup Mode
LM3687 Step-Down DC-DC Converter with Integrated Low Dropout Regulator and Startup Mode
General Description
The LM3687 is a step-down DC-DC converter with an integrated low dropout Linear Regulator optimized for powering
ultra-low voltage circuits from a single Li-Ion cell or 3 cell
NiMH/NiCd batteries. It provides a dual output with fixed output voltages and combined load current up to 750mA in post
regulation mode or 1100mA in independent mode of operation, over an input voltage range from 2.7V to 5.5V. There are
several different fixed output voltage combinations available
(refer to table 'Voltage Options').
The Linear Regulator being driven from the fixed output voltage of the buck converter (post regulation) translates to high
efficiency.
The device offers superior features and performance for mobile phones and similar portable applications with complex
power management systems. Automatic intelligent switching
between PWM low-noise and PFM low-current mode offers
improved efficiency over the full load current range. During
full-power operation, a fixed-frequency 1.8MHz (typ.) PWM
mode drives loads from ~80mA to 750mA max. Hysteretic
PFM mode extends the battery life through reduction of the
quiescent current during light loads and system standby.
The LM3687 also features internal protection against overtemperature, current overload and under-voltage conditions.
Two enable pins allow the separate operation of either the
DC-DC or the Linear Regulator alone or both. If the power
input voltage for the Linear Regulator V
high (e.g. the DC-DC converter is not enabled or starting up)
a startup LDO supplies the Linear Regulator Output from
V
for 50mA rated load current (Startup Mode). If V
BATT
is at the required voltage level, the startup LDO is deactivated
and the main regulator provides 350mA output current. In
shutdown mode (Enable pins pulled low) the device turns off
and reduces battery consumption to 0.1µA (typ.).
The LM3687 is available in a tiny, lead-free (NO PB) 9-bump
micro SMD package. A high switching frequency of 1.8MHz
(typ.) allows the use of tiny surface-mount components. Only
four external components -one inductor and three ceramic
capacitors- are required.
is not sufficiently
IN_LIN
IN_LIN
Features
DC-DC Converter:
750mA maximum load capability
■
1.8MHz PWM fixed switching frequency (typ.)
■
Automatic PFM/PWM mode switching
■
27µA typ. Quiescent Current
■
Internal synchronous rectification for high efficiency
■
Internal soft start
■
Dual Rail Linear Regulator:
Startup Mode
■
Load transients < 25mVpeak typ.
■
Line transients < 1mVpeak typ.
■
Very Low Dropout Voltage: 82mV typ. at 350mA load
■
current
0.7V ≤ V
■
10µA typical IQ from V
■
350mA maximum load capability
■
Combined Common Features:
65µA typical Quiescent Current from V
■
regulators are enabled
750mA maximum combined load capability in post
■
regulation setup (DC-DC 400mA + Linear Regulator
350mA)
1100mA maximum total load capability in independent
■
mode of operation (DC-DC: 750mA, Linear Regulator:
350mA)
Operates from a single Li-Ion cell or 3 cell NiMH/NiCd
■
batteries
Only four tiny surface-mount external components
■
required (one inductor, three ceramic capacitors)
Small 9-bump micro SMD package
■
Over-temperature, current overload and under-voltage
■
protection
IN_LIN
≤ 4.5V
IN_LIN
BATT
if both
Applications
Mobile Phones
■
Hand-Held Radios
■
Personal Digital Assistants
■
Palm-top PCs
■
Portable Instruments
■
Battery Powered Devices
■
© 2008 National Semiconductor Corporation 202101 www.national.com
Typical Application Circuit
LM3687
FIGURE 1. Typical Application Circuit: Linear Regulator as Post Regulator
20210101
FIGURE 2. Typical Application Circuit: Independent Mode of Operation
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20210105
Connection Diagrams
LM3687
Connection Diagram 9-Bump Thin Micro SMD Package
20210104
Top View
20210102
Package Mark
Large Bump, 0.5mm Pitch,
See NS Package TLA09
Note:The actual physical placement of the package marking will vary from part to part. The package marking "X" designates the
date code. "T" is a NSC internal code for die traceability. Both will vary considerably. "BC" identifies the device (part number, option,
etc.)
Pin Descriptions
Pin Number Pin Name Description
A1 PGND Power Ground pin
A2 SGND Signal Ground pin
A3 V
OUT_LIN
B1 SW Switching Node Connection to the internal PFET switch and NFET synchronous rectifier
B2 EN_DCDC Enable Input for the DC-DC converter. The DC-DC converter is in shutdown mode if voltage at this
B3 V
C1 V
IN_LIN
BATT
C2 FB_DCDC Feedback Analog Input for the DC-DC converter. Connect directly to the output filter capacitor.
C3 EN_LIN Enable Input for the linear regulator. The linear regulator is in shutdown mode if voltage at this pin
Voltage Output of the linear regulator
pin is < 0.4V and enabled if > 1.0V. Do not leave this pin floating. Please see section 'Enable
Combinations'.
Power Supply Input for the linear regulator
Power Supply for the DC-DC output stage and internal circuitry. Connect to the input filter capacitor
(see typical application).
is < 0.4V and enabled if > 1.0V. Do not leave this pin floating. Please see section 'Enable
Combinations'.
Voltage Options
DC-DC Converter Output:
V
OUT_DCDC
1.80V 1.50V
1.80V 1.20V
1.80V * 1.30V *
* For availability of these or other output voltage combinations please contact your local NSC sales office
Linear Regulator Output:
V
OUT_LIN
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Enable Combinations
LM3687
EN_DCDC EN_LIN Comments
0 0 No Outputs
0 1 Linear Regulator enabled only *
1 0 DC-DC converter enabled only
1 1 DC-DC converter and linear regulator active *
* Startup Mode:
V
must be higher than V
IN_LIN
If V
IN_LIN
< V
OUT_LIN(NOM)
OUT_LIN(NOM)
+ 100mV (100mV hysteresis), the startup LDO (I
+ 200mV in order to enable the main regulator (I
= 50mA) is active, supplied from V
MAX
= 350mA).
MAX
BATT
For example in the typical post regulation application the LDO will remain in startup mode until the DC-DC converter has ramped
up its output voltage.
Order Information
.
Output Voltage Option
V
OUT_DCDC
V
OUT_LIN
1.80V 1.50V
1.80V 1.20V
1.80V * 1.30V *
Order Number Package Marking Supplied as Flow
LM3687TL-1815 S9
LM3687TLX-1815
S9 3000 units, tape and
LM3687TL-1812 SB
LM3687TLX-1812 SB
LM3687TL-1813 tbd
LM3687TLX-1813 tbd
250 units, tape and reel,
reel, lead free
250 units, tape and reel,
3000 units, tape and
reel, lead free
250 units, tape and reel,
3000 units, tape and
reel, lead free
* For availability or other output voltage combinations please contact your local NSC sales office
lead free
lead free
lead free
NOPB
NOPB
NOPB
NOPB
NOPB
NOPB
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LM3687
Absolute Maximum Ratings (Notes 2, 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
, V
IN_LIN
V
IN_LIN
V
IN_LIN
Enable pins,
Feedback pin,
SW pin
Continuous Power Dissipation
(Note 3) Internally Limited
Junction Temperature (T
Storage Temperature Range -65°C to + 150°C
Package Peak Reflow Temperature
(Pb-free, 10-20 sec.) (Note 4) 260°C
ESD Rating (Note 5)
Human Body Model: 2.0kV
Machine Model 200V
pins: Voltage to GND,
BATT
≤ V
BATT
pin to V
pin 0.2V
BATT
-0.2V to 6.0V
(GND-0.2V) to
(V
BATT
) 150°C
J-MAX
+0.2V) with
6.0V max
Operating Ratings
(Notes 1, 2)
Input Voltage Range V
(Note 12)
BATT
(≥V
2.7V to 5.5V
OUT_LIN(NOM)
+ 1.5V
and
≥V
OUT_DCDC(NOM)
1.0V)
Input Voltage Range V
IN_LIN
(V
OUT_LIN(NOM)
+ 0.25V)
to 4.5V
Junction Temperature (TJ) Range -30°C to + 125°C
Ambient Temperature (TA) Range
-30°C to + 125°C
(Note 6)
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA), for 4 layer board
(Note 7)
Micro SMD 9 70°C/W
+
ESD Caution Notice
National Semiconductor recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper
ESD handling techniques can result in damage.
Electrical Characteristics (Notes 2, 8) Typical values and limits appearing in standard typeface are for T
25°C. Limits appearing in boldface type apply over the full operating temperature range: -30°C ≤ TJ ≤ +125°C. Unless otherwise
noted, V
10µF, C
= V
IN_LIN
VOUT_LIN
OUT_LIN(NOM)
= 2.2µF, C
+ 0.3V, V
= 1.0µF, L = 2.2µH.
VIN_LIN
BATT
= 3.6V, I
OUT_LIN
= 1mA, V
EN_DCDC
= V
EN_LIN
= V
BATT
, C
VBATT
= 4.7µF, C
VOUT_DCDC
=
A
=
DC-DC Converter (Note 11)
Symbol Parameter Conditions Typical Limit Units
Min Max
V
FB_DCDC
R
DSON(P)
R
DSON(N)
I
LIM_DCDC
F
OSC
Feedback Voltage
Accuracy
Line Regulation
Load Regulation
Pin-Pin Resistance for
PFET
Pin-Pin Resistance for
NFET
Switch Peak Current
Limit
Internal Oscillator
Frequency
PWM Mode -2.5 +2.5 %
V
OUT_DCDC
+ 1.0V ≤ V
BATT
≤ 5.5V, I
OUT_DCDC
0.06 %/V
= 150mA
100mA ≤ I
OUT_DCDC
≤ 750mA
0.0005 %/mA
280 500
200 400
Open loop (Note 14) 1172 994 1380 mA
PWM Mode 1.8 1.3 2.3 MHz
mΩ
mΩ
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Linear Regulator, Normal Mode
LM3687
ΔV
V
OUT_LIN(NOM)
ΔV
ΔV
ΔV
ΔV
ΔV
V
DO_VIN_LIN
I
Q_VIN_LIN
I
SC_LIN
PSRR
E
N
ΔV
ΔV
Symbol Parameter Condition Typ Limit Units
Min Max
OUT_LIN
OUT_LIN
IN_LIN
OUT_LIN
BATT
OUT_LIN
/
/
/
/ ΔmA
Output Voltage
Accuracy
Line Regulation Error
Load Regulation Error
Output Voltage
Dropout
(Note 10)
Quiescent Current into
V
IN_LIN
Shutdown Current into
V
IN_LIN
Output Current
In startup and normal mode
V
IN_LIN
4.5V, V
V
BATT
= V
OUT_LIN(NOM)
= 4.5V
BATT
= V
OUT_LIN(NOM)
+ 0.3V to
+ 1.5V
-1.5
-2.0
0.3 1 mV/V
0.5 3.1
1.5
2.0
(≥2.7V) to 5.5V
I
= 1mA to 350mA 10 60 µV/mA
OUT_LIN
I
= 350mA ,
OUT_LIN
V
BATT
= V
OUT_LIN(NOM)
+ 1.5V
(≥2.7V) 85
I
= 150mA ,
OUT_LIN
V
BATT
= V
OUT_LIN(NOM)
+ 1.3V
(≥2.7V) 42
I
= 0mA 10 28 µA
OUT_LIN
V
= 0V 0.1 1 µA
EN_LIN
V
= 0V 500 350 mA
OUT_LIN
200 mV
100 mV
(short circuit)
Power Supply
Rejection Ratio
Output Noise linear
Sine modulated V
f = 10Hz
f = 100Hz
f = 1kHz
Sine modulated V
f = 10Hz
f = 100Hz
f = 1kHz
f = 10kHz
10Hz - 100kHz 100 µV
BATT
IN
,
70
65
45
80
90
95
85
regulator
V
OUT_LIN
OUT_LIN
Dynamic line transient
response V
IN_LIN
Dynamic line transient
response V
BATT
Dynamic load transient
response
= V
IN_LIN
V
OUT_LIN(NOM)
OUT_LIN(NOM)
+ 0.9V
tr, tf = 10µs
V
= V
BATT
V
OUT_LIN(NOM)
OUT_LIN(NOM)
+ 2.1V
tr, tf = 10µs
Pulsed load 0 ... 350mA
di/dt = 350mA/1µs
+ 0.3V to
+ 1.5V to
±1 mVp
±15 mVp
±30 mVp
%
%
dB
dB
RMS
Startup LDO
Symbol Parameter Conditions Typical Limit Units
Min Max
I
OUT
I
SC_LIN
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Rated output current 50 mA
Output Current (short
V
OUT_LIN
= 0V 100 50 mA
circuit)
System Parameters Supply
LM3687
Symbol Parameter Conditions Typical
I
Q_VBATT
Quiescent current
into V
BATT
EN_LIN = low, EN_DCDC = high, I
I
= 0mA, DC-DC is not switching
OUT_LIN
(FB_DCDC forced higher than V
OUT_DCDC
OUT_DCDC
)
=
27
Limit
Min Max
60 µA
EN_LIN = high, EN_DCDC = low 55 µA
EN_LIN = EN_DCDC = high 65 µA
Shutdown current into
V
BATT
V
EN_DCDC
= V
EN_LIN
-30°C ≤ TJ ≤ +85°C
= 0V
0.1
5 µA
Under-Voltage Protection
Symbol Parameter Conditions Typical Limit Units
Min Max
V
BATT_UVP
V
BATT_EN
Under-Voltage
Lockout
System Enable
Voltage
2.41 V
2.65 V
Enable Pins (EN_DCDC, EN_LIN)
Symbol Parameter Conditions Typical
I
EN
V
IH
V
IL
Enable pin input
current
Logic High voltage
level
Logic Low voltage
level
0.01 1 µA
1.0 V
0.4 V
Limit
Min Max
Units
Units
Thermal Protection
Symbol Parameter Conditions Typical
T
SHDN
(Note 15)
ΔT
SHDN
Thermal-Shutdown
Temperature
Thermal-Shutdown
Hysteresis
160 °C
20 °C
Limit
Min Max
Units
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